As a cold drizzle soaks this mile-high mountain redoubt, Pakistan Army Maj. Mohammed Najeeb peers far across the steep rocky gorge through high-power binoculars. There, perched high above raging rapids and a bombed-out bridge, an Indian sentry can be seen peering back from his own blockhouse and bunker complex. "This is the crucial point," said Najeeb. "This is the old invasion route for Kashmir."

India and Pakistan traded fire across their border Friday, and India again accused Pakistan of escalating clashes to cover the infiltration of militants into the disputed Kashmir region. "After exercising utmost restraint, our troops retaliated appropriately," an Indian Defense Ministry statement said. Tensions have been rising after India's underground nuclear tests last week, which left Pakistan weighing whether to respond with nuclear tests of its own.

In this frozen wasteland, the historic rivalry between India and Pakistan seems as enduring as the glacial ice. On the Siachen Glacier, where nearby peaks reach 23,000 feet and temperatures drop to 50 below zero, the frostbitten armies of two implacable foes have faced each other for 15 years in a conflict both bloody and surreal. Cold and crevasses kill more troops than opposing armies.

Bush administration officials watched warily Tuesday as nuclear-armed rivals India and Pakistan moved more combat troops and missiles closer to their shared border and escalated their war of words. But U.S. officials said the crisis might be defused in coming days because Pakistan appears to have launched a crackdown against several Islamic militant groups, two of which India blames for the attempted suicide bombing of the Parliament in New Delhi two weeks ago.

Pakistani forces shot down at least one Indian jet fighter along the two nations' disputed Himalayan border Thursday, driving tensions between the historic rivals to dangerous new levels. As Indian jets launched fresh attacks on Islamic guerrillas inside Kashmir, a region claimed by both countries, Pakistani officials said their forces downed two Indian jets over Pakistan and captured a pilot.